In the manufacture of automobiles, it is common practice to provide specific datum points in the structure to assist in "jigging" the vehicle during manufacture, and in checking the dimensional accuracy of the finished product. These datum points can take various forms such as holes in the chassis, male or female threaded members such as bolt heads, nuts or studs, and other formations such as pins, lugs, and suspension mounting points. They may be oriented in vertical or horizontal planes, or at intermediate angles. They also vary significantly from model to model according to various design parameters and practical convenience. In all cases, however, they are accurately positioned in known locations and the design specification of each vehicle normally includes a table of dimensions which correlate the various datum points.
Numerous types of known apparatus purport to provide an indication of the extent of misalignment, to facilitate the evaluation and repair of damaged or potentially damaged vehicles. However, these have been found to be inadequate in various respects.
More particularly, one type of prior art device consists in a peripheral reference frame rotatably or otherwise connected to a floor mounted anchorage assembly to extend generally around the vehicle. Such devices are not adapted for direct connection to the datum points on the vehicle, and so are not able to provide an accurate and direct quantitative correlation between the various datum points and the manufacturer's specifications.
Moreover, such devices tend to be structurally flimsy, and are inherently prone to excessive deflection, particularly adjacent the front and rear extremities of the vehicle, where accurate measurement is critical. Also, in such measurement systems it is difficult or impossible to align the vehicle precisely with the floor mounted anchorage assembly. For both these reasons, such devices are not capable even of providing accurate and consistent comparative measurements between corresponding points on the vehicle to provide a reliable measure of the degree of misalignment.
Other known devices are adapted for direct connection to datum points and so to a limited extent are capable of directly correlating measurements between datum points on the vehicle with dimensional specifications provided by the manufacturer. However, most such devices are complex, expensive, cumbersome, involve a relatively large number of components, and are generally difficult and time consuming to use. Furthermore, most known devices of this type are only capable of providing quantitative measurements between longitudinally or transversely spaced datum points. As such, they cannot measure or compare diagonals directly and so cannot accurately detect parallelogram type deformation in the vehicle frame. Moreover, a number of manufacturers actually specify distances in their data sheets in terms of diagonals, and these cannot be directly correlated using this known type of apparatus. Furthermore, prior art systems of this type are generally only capable of attachment to certain specific types of datum points, and so tend not to be applicable to a wide variety of vehicles.
For certain makes and models of vehicle dedicated jigs, frames, or the like are available. Again, however, these tend to be expensive and require considerable set-up time. Consequently, such devices tend only to be appropriate and worthwhile in connection with major repairs and again, they are not applicable to a wide range of vehicles.
More simple devices in the form of hand-held trammels are also known. However, these too are limited in their practical applicability. They require constant re-checking and frequently two operators are required, one to support and position each end. There are also practical limits in terms of the distances which such devices are capable of measuring. In this regard, fixed length trammels tend to be excessively long and cumbersome to provide accurate measurements of relatively short dimensions and even telescopic arrangements tend to be limited in this respect relative to the length of the longest telescoping element.
It is therefore an object of the present invention to provide an improved apparatus which overcomes or substantially ameliorates at least some of these disadvantages of the prior art.